Processes for the conjugation of the double bonds of polyunsaturated unconjugated fatty acids have found their main application in the field paints and varnishes. Oils comprised of triglycerides of conjugated fatty acids are known as drying oils. Drying oils have value because of their ability to polymerize or "dry" after they have been applied to a surface to form tough, adherent and abrasion resistant films. Tung oil is an example of a naturally occurring oil containing significant levels of conjugated fatty acids.
Because tung oil is expensive for many industrial applications, research was directed towards finding a substitute. In the 1930's, it was found that conjugated fatty acids were present in oil products subjected to prolonged saponification, as originally described by Moore, J. Biochem., 31: 142 (1937). This finding led to the development of several alkali isomerization processes for the production of conjugated fatty acids from various sources of polyunsaturated fatty acids.
In alkali isomerization the fatty acids are exposed to heat, pressure and a metal hydroxide or oxide in nonaqueous or aqueous environments, resulting in the formation of conjugated isomers. Other methods have been described which utilize metal catalysts, which is not as efficient in the production of conjugated double bonds. It was found that isomerization could be achieved more rapidly in the presence of higher molecular weight solvent. Kass, et al., J. Am. Chem. Soc., 61: 4829 (1939) and U.S. Pat. No. 2,487,890 (1950) showed that replacement of ethanol with ethylene glycol resulted in both an increase in conjugation in less time. U.S. Pat. No. 2,350,583 and British Patent No. 558,881 (1944) achieved conjugation by reacting fatty acid soaps of an oil with an excess of aqueous alkali at 200-230 degrees C. and increased pressure.
Among the processes known to effect isomerization without utilizing an aqueous alkali system, is a nickel-carbon catalytic method, as described by Radlove, et al., Ind. Eng. Chem.38: 997 (1946). A variation of this method utilizes platinum or palladium-carbon as catalysts.
Purified conjugated linoleic acid ("CLA") has recently been shown in several studies to have unique properties when used as a food additive. Purified CLA appears to affect fat deposition in animals. Purified CLA both increases the lean to fat ratio, effectively reducing body fat, and increases feed conversion efficiency. An additional advantage of feeding CLA is that it appears to modulate immune responses under certain conditions. In laboratory animal studies CLA has been shown to prevent weight loss due to immune stimulation and to treat immune hypersensitivity.
The purified CLA utilized in prior studies as an animal feed additive was obtained by small scale laboratory procedures involving production of CLA from highly purified linoleic acid. Laboratory and pilot scale oil refining systems have been described for preparation of purified seed oils. For example Sullivan, J. Am. Oil Chemists' Soc., 53: 359 (1976), describes a laboratory semi-pilot steam refining system made entirely of glass.
While these systems are adequate for producing quantities of conjugated fatty acids for laboratory studies, or even clinical trials, they are not suitable for commercial scale bulk production. On the other hand, the large scale systems available to produce industrial quantities of conjugated acids, as in classical drying oils, cannot be run inexpensively enough to produce material for bulk animal feeds. The standard degumming, refining, and dehydration steps necessary to obtain nutritionally safe edible conjugated oils for livestock feeding, are prohibitively complex and expensive. (See Braae, J. Am. Oil Chemists' Soc., 53: 353 (1976) for a discussion of complex degumming processes as practiced on a commercial scale in Europe). Also there are significant losses of product through polymerization of conjugated fatty acids or their precursors at high temperatures.
Economical CLA production in commercial quantities for use in domestic food animal feeds is a desirable objective in light of the nutritional benefits realized on a laboratory scale. Preferably, the CLA is produced directly from a source of raw vegetable oil and not from expensive purified linoleic acid. Further, the process must avoid cost generating superfluous steps, and yet result in a safe and wholesome product palatable to animals.